python-injection 0.8.0

Fast and easy dependency injection framework.

Basic usage

Create an injectable

Note: If the class needs dependencies, these will be resolved when the instance is retrieved.

If you wish to inject a singleton, use singleton decorator.

from injection import singleton

@singleton
class Singleton:
    """ class implementation """

If you wish to inject a new instance each time, use injectable decorator.

from injection import injectable

@injectable
class Injectable:
    """ class implementation """

If you have a constant (such as a global variable) and wish to register it as an injectable, use set_constant function.

from injection import set_constant

app = set_constant(Application())

Inject an instance

To inject one or several instances, use inject decorator. Don't forget to annotate type of parameter to inject.

from injection import inject

@inject
def my_function(instance: Injectable):
    """ function implementation """

If inject decorates a class, it will be applied to the __init__ method. Especially useful for dataclasses:

Note: Doesn't work with Pydantic BaseModel because the signature of the __init__ method doesn't contain the dependencies.

from dataclasses import dataclass

from injection import inject

@inject
@dataclass
class DataClass:
    instance: Injectable = ...

Get an instance

Example with get_instance function:

from injection import get_instance

instance = get_instance(Injectable)

Example with get_lazy_instance function:

from injection import get_lazy_instance

lazy_instance = get_lazy_instance(Injectable)
# ...
instance = ~lazy_instance

Inheritance

In the case of inheritance, you can use the decorator parameter on to link the injection to one or several other classes.

Warning: if the child class is in another file, make sure that file is imported before injection. See load_package function.

Example with one class:

from injection import singleton

class A:
    ...

@singleton(on=A)
class B(A):
    ...

Example with several classes:

from injection import singleton

class A:
    ...

class B(A):
    ...

@singleton(on=(A, B))
class C(B):
    ...

If a class is registered in a package and you want to override it, there is the override parameter:

@singleton
class A:
    ...

# ...

@singleton(on=A, override=True)
class B(A):
    ...

Recipes

A recipe is a function that tells the injector how to construct the instance to be injected. It is important to specify the return type annotation when defining the recipe.

from injection import singleton

@singleton
def my_recipe() -> Singleton:
    """ recipe implementation """